I understand that undo feature is not easy to implement. In real game, there is no undo. However, I won't mess up opponents' bid with my partner's bid in real world, but it's happened several times to me already. I just "overcalled" 4S after RHO opened 1S yesterday (I though my partner opened 1S). I suggest highlighting every bid by the opponents. It would be easier to identify who makes the bid.